RU2350436C2 - Ceramic drill for high-speed drilling - Google Patents

Abstract

FIELD: mechanics, tools.

SUBSTANCE: proposed drill comprises cylindrical shank and working part comprising two main cutting edges and crosswise edge, two cutting teeth and two grooves running, alternating, about the drill axis of rotation. Every cutting tooth has tape, while every groove incorporates main front surface adjoining the said tape and main cutting edge. At least, the drill working part is made in plastic material. Note here that the drill front angle is positive. The drill rear surface passes from every main cutting edge at rear angle making approximately 4° to 10° relative the plane perpendicular to the drill axis of rotation. Two cuts that form two secondary front surfaces of the drill pass from crosswise edge at positive front angles making about 1° to 7° to the drill axis of rotation.

EFFECT: higher drill strength and drilling efficiency.

23 cl, 4 dwg

Description

FIELD OF THE INVENTION

The present invention relates to a drill made of ceramic material. It finds application, in particular, in aviation for high-speed drilling of high-hardness materials, such as heat-resistant materials and, in particular, nickel and cobalt-based superalloys, for example Inconel 718, which are used, in particular, for the manufacture of flange parts in aircraft structures.

State of the art

Currently, ceramic is increasingly used for the manufacture of cutting tools due to its high hardness and ability to withstand high temperatures. Typically, well-known ceramic cutting tools that are capable of providing high-speed machining of high hard materials, such as those described in EP-B1-0477093, are milling cutters and turning tools. Unfortunately, the stresses that can affect the drill (associated with the drilling depth, chip removal, intensity and direction of cutting forces) during the drilling operation exceed the stresses that could affect the turning tool or the milling cutter during milling work. These stresses make it difficult to use ceramic drills for drilling at very high speeds materials with increased hardness.

Many manufacturers' catalogs offer a wide range of ceramic drills. One such drill is described in US-A-5641251. Although these drills provide improved performance compared to conventional drills made of high speed steel or tungsten carbide, their use is limited and they do not provide the possibility of drilling with very high speed hard materials such as superalloys. Due to the low viscosity of ceramic materials, ceramic drills have a lower torsional strength and compression resistance than metal drills, for example, made of tungsten carbide, and with such mechanical characteristics, ceramic-metal drills exhibit brittleness when drilling hard materials or at high feed speeds, or at high cutting speeds. Much work has been done to improve the mechanical properties of ceramic-based materials. In particular, US-A-4,789,277 describes ceramic materials in which fibers (or whiskers) of silicon carbide (SiC) are incorporated to improve their mechanical characteristics. In addition, it is known and recommended that the cutting edges of the drills are always made with zero or negative angles to protect the cutting edges from wear and thus increase the life of the ceramic drill.

The use of such drills is still limited in terms of materials and cutting and feed rates. In cases where the drilled materials have a hardness of heat-resistant materials, such as superalloys based on, for example, nickel or cobalt (having a Vickers hardness number of about 440), and at high cutting and feed speeds, for example, when at a cutting speed exceeding about 400 meters per minute (m / min) and with a feed speed exceeding 0.04 mm per revolution, the torsional force and axial compression force that are generated and act on the drills known from the prior art reach values that inevitably lead to the destruction of drills. In addition, the cutting forces applied by such drills to the workpieces and the friction between the radially outer surfaces of the drills and the inner cylindrical surfaces of the drilled holes result in thermal stresses in the drills and drilled workpieces, which lead to accelerated damage to the drills and deformation of the workpiece when trying to drill solid materials at high speed.

In addition, with increasing depth of the drilled hole, the torsional forces acting on the ceramic drills become larger, primarily due to the increasing increase in the area of the outer surface of the drill, rubbing against the inner cylindrical surface of the drilled hole, and, secondly, due to the fact that when drilling at high speeds, ceramic drills from the prior art are not able to effectively extract a large amount of chips, which leads to the phenomenon of clogging of the drill and, consequently tion of an increase in torsional forces applied to the drill bit, and an increased risk of its destruction. These drawbacks usually make it impossible to drill at a high speed to a depth that exceeds the diameter of the drill.

Disclosure of invention

The objective of the invention is to eliminate the above disadvantages and develop a technical solution that would be simple and low cost and would improve the performance of ceramic drills, and provide the ability to drill solid materials at a very high speed.

To solve this problem, a ceramic drill bit is proposed, containing:

- cylindrical shank; and

- the working part, extending in the axial direction coaxially with the shank and having a free end forming the cutting tip of the drill, the working part having the shape of a truncated cone, the larger base of which is located near the cutting tip of the drill,

moreover, the cutting tip contains two main cutting edges and a Central edge located between the two main cutting edges, while the working part contains two cutting teeth and two grooves passing alternating with each other around the axis of rotation of the drill, cutting teeth and grooves extend from the cutting the tip to the shank, each cutting tooth has a ribbon, and each groove has a main front surface adjacent to the ribbon and to the main cutting edge, at least the working part of the drill is made of ceramic Container material, in this case

- the front angle of the drill is positive;

- the rear surface of the drill extends from each major cutting edge at a rear angle of approximately 4 ° to 10 ° relative to a plane perpendicular to the axis of rotation of the drill; and

- two cutouts forming two secondary front surfaces extend from the center edge of the drill at positive rake angles of approximately 1 ° to 7 ° relative to the axis of rotation of the drill.

In an embodiment of the invention, the cutting teeth and grooves are spirally curled around the axis of rotation of the drill at an angle of inclination of the helix of approximately 20 ° to 30 °, and preferably approximately 20 ° to 25 ° relative to the axis of the drill.

In another embodiment, the taper angle of the working part is from about 1 ° to 5 °, and preferably from about 2 ° to 4 °.

In another embodiment, the width of each ribbon is less than one tenth and preferably equal to or less than one twentieth of the outer diameter of the working part.

The combination of dimensional and geometric characteristics of the drill according to the invention provides several advantages.

One of these advantages is a significant reduction in the torsional and compression forces applied to the drill, which prevents it from breaking or shearing when drilling high-speed materials such as nickel and cobalt based superalloys at high speed. To reduce the torsional forces without reducing the strength characteristics of the drill, different solutions are used, one of which relates to limiting the width of the chamfers to reduce the frictional moment between the drill and the cylindrical wall of the drilled hole. The taper of the working part of the drill, approximately 1 ° to 3 °, also helps to reduce the frictional moment between the drill and the wall of the drilled hole, while the ribbons come into contact with the inner cylindrical wall of the drilled hole only near the cutting tip of the drill. In contrast to the practice of manufacturing ceramic drills of the prior art, the front angles of the drill according to the invention are positive and are approximately 4 ° to 10 ° relative to the axis of the drill, thereby reducing cutting forces and, therefore, reduced torsional forces acting on the drill. According to the prior art, the rake angles are zero or even negative to reduce wear on the cutting edges. The reduction of cutting forces and friction between the drill and the walls of the drilled hole also makes it possible to reduce the thermal energy generated during drilling, which allows drilling of very hard materials at high speed without damaging the drill or workpiece.

The compressive forces that act on the drill during drilling are reduced due to two cuts formed starting from the central edge of the ceramic-metal drill. The usual central edges of the ceramic-metal drills do not have a rake angle and, therefore, they provide a significant resistance to the axial movement of the drill. The presence of cutouts allows you to modify the Central edge so that it becomes a cutting edge having two positive rake angles of approximately 1 ° to 7 ° relative to the axis of the drill.

According to the invention, and to reduce the risk of collapse or cutting of the drill, the cutting teeth and grooves have a spiral configuration, allowing the drill to better withstand the torsional forces that affect it, without compromising its other strength characteristics. The spiral configuration of grooves having a helix angle of less than 25 ° allows for good chip removal regardless of the cutting speed and at drilling depths that may exceed the outer diameter of the drill.

In contrast to what might be expected, thermal stresses and material spoilage at the edge of the hole remain negligible and are limited to a depth of several hundred micrometers (microns). The produced chips turn red when they exit the hole, which means that its temperature is around 1000 ° C. It can be concluded that the energy produced during high-speed drilling, for the most part, passes into the chips and is extracted by the chips. In most cases, drilled workpieces are left unfinished. In contrast, with respect to workpieces that are subjected to high stresses, such as rotors of turbojets, holes made during drilling are subsequently subjected to final finishing by conventional means. In any case, high-speed drilling using the drill of the invention is beneficial.

According to other features of the invention, the helix angle of the grooves and cutting teeth is preferably from about 20 ° to 25 °, while the working part of the drill has a taper angle of about 1 °, each ribbon has a width of less than about one twentieth of the outer diameter drill, the rear surface extends from each cutting edge at an angle of less than 12 ° relative to the plane perpendicular to the axis of the drill, and the specified angle is preferably less than 8 °, This may also be formed undercut surface extending in line with each rear surface. Each cutting edge of the drill and the leading edge of each ribbon, forming the intersection of each ribbon and the main front surface, is rounded with a radius of approximately 2 microns to 40 microns. The corners of the cutting edges can also be chamfered by approximately 0.5 millimeters (mm) at an angle of about 20 ° relative to the axis of the drill. These additional features serve to reduce torsional and compression forces acting on the ceramic drill. They also serve to reduce the amount of energy produced by drilling at a high speed, as well as to improve the dispersion of said energy with chips.

According to another preferred feature, the angle at the tip of the drill corresponding to the angle formed between the two main cutting edges is from about 140 ° to 155 °. This feature provides self-centering of the drill and, therefore, eliminates the need for marking operations to center the drill.

According to other features of the drill according to the invention:

- each ribbon has a width of 0.2 mm to 0.8 mm, and preferably from 0.4 mm to 0.8 mm;

- the shank and the working part of the drill are made of ceramic material;

- the ceramic material is selected based on alumina, zirconia, silicon nitride or a mixture of ceramic materials;

- ceramic material reinforced with silicon carbide (SiC) fibers; and

the drill is adapted for drilling heat-resistant materials, such as, for example, aviation materials based on nickel or cobalt, and, in particular, based on Inconel 718 having a Vickers hardness number of about 440.

The problem is also solved by a drilling method using a ceramic drill of the type described above, according to which, for high-speed drilling of heat-resistant aircraft materials based on cobalt and nickel, the peripheral cutting speed of the drill is from about 400 m / min to 1000 m / min, and the feed speed of the drill is from 0.04 to 0.1 mm per revolution. These ranges determine the conditions under which the ceramic drill of the invention can be used without the risk of accelerated wear or fracture of the drill, and which enable good chip removal and provide good heat dissipation with the chip. For optimal conditions of use, the peripheral cutting speed of the drill is approximately 400 m / min to 600 m / min.

According to other features of the method of the invention, drilling is carried out dry without the use of lubricant, and it does not require a preliminary marking operation to center the drill. The use of lubricant when drilling with a drill according to the invention is not recommended because it degrades the characteristics of the drill in terms of cutting parameters and service life.

Depending on the desired final state of the surface, in order to obtain a completed hole, it may be sufficient to perform one drilling operation without performing a preliminary marking operation and without performing a subsequent finishing operation. Since the drilling speed is high and since the number of drilling operations is reduced, the drill according to the invention can significantly reduce the time required for drilling high hard materials. Compared to drills known from the prior art that do not allow drilling of high hard materials at such high speeds, the duration of a drill operation according to the invention is reduced by at least 5 times.

According to other features of the invention, the method is applicable for drilling heat-resistant materials, in particular aviation materials based on nickel or cobalt, and possibly based on an Inconel 718 material having a Vickers hardness number of about 440, and drilling constitutes a roughing operation.

Brief Description of the Drawings

The invention is further explained in the description of the options for its implementation with reference to the accompanying figures of the drawings, including:

Figure 1 is a schematic side view of a drill according to the invention;

Figure 2 is a schematic view of the front end of the drill shown in figure 1;

FIG. 3 is a side view of a portion of the drill of FIG. 1, visible in direction A of FIG. 2; and

FIG. 4 is a side view of a portion of the drill of FIG. 1, visible in direction B of FIG. 2.

The implementation of the invention

As an example, FIGS. 1-4 show a one-piece ceramic drill for high-speed drilling of very high strength materials, such as heat-resistant aircraft materials made from superalloys and, in particular, from Inconel 718.

This ceramic drill 1 contains (Fig. 1) a cylindrical shank 2 and a working part 3 extending from the shank along the axis 4 of the drill. The shank includes an annular groove 5 for gripping the chuck of a mechanical machine (not shown). The free end 6 of the cylindrical shank oriented along the axis ends with a chamfer 7 to facilitate insertion of the shank into the chuck of the machine tool.

The working part 3 of the drill 1 contains two cutting teeth 8 and two grooves 9 passing alternately with each other around the axis 4 from the axial end 10 of the drill 1, which is removed from the shank 2 and is called the cutting tip of the drill. The cutting teeth 8 and the grooves 9 are curled in a spiral around the axis 4 at an angle 11 of the inclination of the helix, which is less than or equal to approximately 25 °.

Each cutting tooth 8 contains a ribbon 12 for sliding along the inner wall of the drilled hole and the rear surface 13, which have a spiral configuration. According to the invention, each ribbon 12 has a width 14 that is less than or equal to approximately one tenth of the diameter 15 of the working part 3 of the drill 1. Each groove 9 has a main cutting surface 16 adjacent to the ribbon 12. The intersection between the ribbon 12 and the main cutting surface 16 forms an edge, called the leading edge 17 of the ribbon 12.

Each ribbon 12 extends near the cutting tip 10 of the drill 1 by the main cutting edge 18. The two main cutting edges are separated by the central edge 19. The angle 20 at the apex, formed between the two main cutting edges, is from about 140 ° to 155 °. Each main cutting edge 18 is formed by the intersection of the main front surface 16 of the groove 9 and the rear surface 21 at an angle of less than about 10 ° with respect to a plane perpendicular to the axis 4 of the drill. Each rear surface 21 extends from the main cutting edge 18 at a rear angle of approximately 4 ° to 10 °, and preferably approximately 6 ° to 8 °, relative to a plane perpendicular to the axis 4 of the drill 1. A positive or negative angle is determined by the orientation of the front surface 16 relative to the cutting direction 23: when the front surface deviates from the cutting edge in the cutting direction 23, the rake angle is negative, and conversely, when the front surface 16 deviates from the cutting edge in to the board opposite to the cutting direction 23, the rake angle 22 is positive.

Each corner 24 of the drill, formed by the intersection between the main cutting edge 18 and the leading edge 17 of the tape 12, includes a bevel 25 of approximately 0.5 mm and approximately 20 ° relative to the axis 4 of the drill.

The working part 3 of the drill 1 has a common external configuration in the form of a truncated cone. The larger base of the truncated cone is near the cutting tip 10, and the taper angle 26 of the working portion 3 is from about 1 ° to 3 °.

Two secondary front surfaces 28 formed by two cutouts 27 (FIGS. 1, 2 and 4) extend from the center edge of the drill 19 at a positive rake angle 29 (FIG. 4) of approximately 1 ° to 7 ° relative to the axis 4 of the drill. Thus, the center edge 19 according to the invention includes two secondary cutting edges.

The main and secondary cutting edges 18 and 19 of the drill 1 and the leading edge 17 of each ribbon 12 are rounded with a radius of 2 μm to 40 μm.

The ceramic material constituting the whole drill 1 is made on the basis of alumina reinforced with silicon carbide (SiC) fibers.

In an embodiment of the drill according to the invention, the ceramic material can be made on the basis of zirconium dioxide, based on silicon nitride or a mixture of ceramic materials representing zirconium dioxide and silicon nitride, possibly reinforced with silicon carbide fibers.

In another embodiment of the invention, the working part 3 and the shank 2 of the drill 1 are two elements that are made separately of different materials and are connected to each other, for example, by brazing. The working part 3 of the drill in this case is made of ceramic material, while the shank 1 of the drill is made of a material having greater strength than the ceramic material, so that it can better withstand the forces acting on the drill 1. For example, the material for making the shank 2 of the drill 1 can be tungsten carbide.

To improve the performance of the drill 1 according to the present invention, the helix inclination angle 11 is preferably from about 20 ° to 25 °, the working part 3 has a taper angle 26 of about 1 °, each ribbon 12 has a width 14 that is less than about one twentieth part of the outer diameter 15 of the working part 3, each rear surface 21 has an angle of about 8 ° relative to a plane perpendicular to the axis 4 of the drill 1, and each rear surface 21 can also be extended by the trimmed surface 30.

In an embodiment of a drill 1 according to the invention, the width 14 of each ribbon 12 is approximately 0.5 mm.

The ceramic drill 1 according to the invention is particularly well adapted for drilling heat-resistant materials, such as heat-resistant aircraft materials based on nickel or cobalt and generally referred to as “superalloys”. For example, an Inconel 718 can be drilled at a very high speed, having a Vickers hardness number of about 440. According to the invention, the peripheral cutting speed of the drill is from about 400 m / min to 1000 m / min, and the feed rate is from about 0.04 to 0.1 mm per revolution when drilling solid materials such as Inconel 718, which makes it possible to significantly reduce the stresses affecting the drill 1 both thermally and mechanically in the form of torsional forces and compression forces. At these speeds, thermal stresses are reduced by heat dissipation using chips that quickly transfer this heat energy out of the hole being drilled. For optimal conditions of use, the peripheral cutting speed of the drill should be approximately 400 m / min to 600 m / min. Using a drill beyond the recommended speed range results in accelerated wear on the drill.

According to another feature of the invention, drilling is carried out dry, without lubrication, and it is a roughing operation that does not require any preliminary marking operation to center the drill.

Depending on the desired final state of the surface, a single drilling operation may be sufficient to complete the hole without any preliminary marking operation and without any subsequent finishing operation.

Claims (23)

1. Ceramic drill bit containing a cylindrical shank and a working part extending axially coaxially with the shank and having a free end forming a cutting tip of the drill, the working part having the shape of a truncated cone, the larger base of which is located near the cutting tip of the drill, and the cutting tip contains two main cutting edges and a transverse edge located between the two main cutting edges, the working part contains two cutting teeth and two grooves passing alternating between ug with another, around the axis of rotation of the drill, cutting teeth and grooves extend from the cutting tip to the shank, each cutting tooth has a band and each groove contains a main front surface adjacent to the ribbon and to the main cutting edge, at least the working part of the drill is made of ceramic material, while the front angle of the drill is made positive, the rear surface of the drill passes from each main cutting edge at a rear angle of approximately 4 to 10 ° relative to the plane, perpendicular yarnoy tool rotation axis, and two notches forming two secondary front surface of the drill held on the transverse edge at a positive rake angle is from about 1 to 7 ° relative to the tool rotation axis. 2. The drill according to claim 1, in which the cutting teeth and grooves are curled in a spiral around the axis of rotation of the drill at an angle of inclination of the helix of approximately 20 to 30 ° relative to the axis of the drill. 3. The drill according to claim 2, in which the angle of inclination of the helix is approximately 20 to 25 °. 4. The drill according to claim 1, in which the taper angle of the working part is approximately 1 to 5 °. 5. The drill according to claim 4, in which the taper angle of the working part is from about 2 to 4 °. 6. The drill according to claim 1, in which the width of each ribbon is from 0.2 to 0.8 mm 7. The drill according to claim 6, in which the width of each ribbon is from 0.4 to 0.8 mm 8. The drill according to claim 1, in which each ribbon has a width that is less than or equal to approximately one twentieth of the outer diameter of the drill. 9. The drill according to claim 1, in which the rear angle is from 6 to 8 ° relative to the plane perpendicular to the axis of rotation of the drill. 10. The drill according to claim 1, in which each rear surface is continued by a clipped surface. 11. The drill according to claim 1, in which each main cutting edge of the drill and the front edge of each ribbon are rounded with a radius of approximately 2 to 40 microns. 12. The drill according to claim 1, in which the intersection between the main cutting edge and the front edge of the ribbon forms an angle having a bevel of approximately 0.5 mm at an angle of approximately 20 ° relative to the axis of the drill. 13. The drill according to claim 1, in which the angle at the top of the drill corresponds to the angle formed by the two main cutting edges, comprising from about 140 to 155 °. 14. The drill according to claim 1, in which the shank and the working part of the drill are made of ceramic material. 15. The drill according to claim 1, in which a ceramic material based on alumina, zirconia, silicon nitride or a mixture of these ceramic materials is used as the material of its ceramic cutting tip. 16. The drill according to claim 1, in which the ceramic material is reinforced with silicon carbide fibers. 17. The drill according to claim 1, intended for drilling heat-resistant materials, in particular aviation materials based on nickel and cobalt, for example, Inconel 718 material having a Vickers hardness number of about 440. 18. The drilling method using the ceramic drill according to claim 1, according to which the peripheral cutting speed of the drill is selected from about 400 to 1000 m / min, and the feed of the drill is selected from 0.04 to 0.1 mm per revolution. 19. The method according to p, according to which the peripheral cutting speed of the drill is selected from approximately 400 to 600 m / min 20. The method according to p, according to which the drilling is performed dry. 21. The method according to p, according to which the drilling is intended for roughing operations, which does not require prior alignment. 22. The method according to p, according to which, to obtain a completed hole perform one drilling operation. 23. The method according to p, according to which the drilling depth is selected in excess of the diameter of the working part of the drill.

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